1. Field of the Invention
The present invention relates to a device for purifying the exhaust gas of an internal combustion engine.
2. Description of the Related Art
The exhaust gas of an internal combustion engine and, particularly, of a diesel engine, contains particulates comprising carbon as a chief component. Particulates are harmful materials and thus it has been suggested that a particulate filter should be arranged in the exhaust system to trap particulates before they are emitted into the atmosphere. In such a particulate filter, the trapped particulates must be burned and removed to prevent resistance to the exhaust gas from increasing due to the blocked meshes.
In such a regeneration of the particulate filter, if the temperature of the particulates becomes about 600 degrees C., they ignite and burn. However, usually, the temperature of an exhaust gas of a diesel engine is considerably lower than 600 degrees C. and thus heating means is required to heat the particulate filter itself.
Japanese Examined Patent Publication No. 7-106290 discloses that if one of the platinum group metals and one of the oxides of the alkali earth metals are carried on the filter, the particulates on the filter burn and disappear successively at about 400 degrees C. 400 degrees C. is a usual temperature of the exhaust gas of a diesel engine.
However, when the above-mentioned filter is used, the temperature of the exhaust gas is not always about 400 degrees C. Further, a large amount of particulates can be discharged from the engine. Thus, particulates that cannot be burned and removed each time can be deposited on the filter.
In this filter, if a certain amount of particulates is deposited on the filter, the ability to burn and remove particulates drops much so that the filter cannot be regenerated by itself. Thus, if such a filter is merely arranged in the exhaust system, blocking of the filter meshes can occur relative quickly.
Therefore, an object of the present invention is to provide a device, for purifying the exhaust gas of an internal combustion engine, which can prevent blocking of the particulate filter meshes by the trapped particulates thereon.
According to the present invention, there is provided a first device for purifying the exhaust gas of an internal combustion engine comprising a particulate filter arranged in the exhaust system on which the trapped particulates are oxidized, and reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, wherein the particulate filter has a trapping wall, the trapping wall has a first trapping surface and a second trapping surface, the reversing means reverses the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter so that the first trapping surface and the second trapping surface are used alternately to trap the particulates, and the device further comprises improving means for improving the amount of particulates that can be oxidized and removed on the particulate filter.
According to the present invention, there is provided a second device for purifying the exhaust gas of an internal combustion engine comprising a particulate filter arranged in the exhaust system on which the trapped particulates are oxidized, and reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, wherein the particulate filter has a trapping wall, the trapping wall has a first trapping surface and a second trapping surface, the reversing means reverses the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter so that the first trapping surface and the second trapping surface are used alternately to trap the particulates, and the both end portions of the particulate filter have an oxidization ability higher than that of the central portion of said particulate filter.
According to the present invention, there is provided a third device for purifying the exhaust gas of an internal combustion engine comprising a particulate filter arranged in the exhaust system on which the trapped particulates are oxidized, and reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, wherein the particulate filter carries an active-oxygen releasing agent, active-oxygen released from the active-oxygen releasing agent oxidizes the trapped particulates, the active-oxygen releasing agent holds NOX to combine the NOX with oxygen when excessive oxygen is present in the surroundings and releases to decompose the combined NOX and oxygen into NOX and active-oxygen when the oxygen concentration in the surroundings drops, the particulate filter has a trapping wall, the trapping wall has a first trapping surface and a second trapping surface, the reversing means reverses the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter so that the first trapping surface and the second trapping surface are used alternately to trap the particulates, and the device further comprises improving means for improving the amount of particulates that can be oxidized and removed of the particulate filter by making the oxygen concentration in the surroundings drop to release NOX from the active-oxygen releasing agent.
The present invention will be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.